DESCRIPTION

The idn_nameinit() function initializes the library. It also sets default configuration if load_file is 0, otherwise it tries to read a configuration file. If idn_nameinit() is called more than once, the library initialization will take place only at the first
call while the actual configuration procedure will occur at every call.

If there are no errors, idn_nameinit() returns idn_success. Otherwise, the returned value indicates the cause of the error. See the section RETURN VALUES below for the error codes.

It is usually not necessary to call this function explicitly because it is implicitly called when idn_encodename(), idn_decodename(), or idn_decodename2() is first called without prior calling of idn_nameinit().

The idn_encodename() function performs name preparation and encoding conversion on the internationalized domain name specified by from, and stores the result to to, whose length is specified by tolen. The actions argument is a bitwise-OR of the following macros, specifying which subprocesses in the encoding process are to be employed.

IDN_ENCODE_APP is used for ordinary application to encode a domain name. It performs IDN_ASCCHECK in addition with IDN_ENCODE_QUERY. IDN_ENCODE_STORED is used to encode a ``stored string'' (see the IDNA specification). It
performs IDN_ENCODE_APP plus IDN_UNASCHECK.

The idn_decodename() function performs the reverse of idn_encodename(). It converts the internationalized domain name given by from, which is represented in a special encoding called ACE (ASCII Compatible Encoding), to the application's
local codeset and stores in to, whose length is specified by tolen. As in idn_encodename(), actions is a bitwise-OR of the following macros.

IDN_DECODE_APP is used for ordinary application to decode a domain name. It performs IDN_ASCCHECK in addition to IDN_DECODE_QUERY. IDN_DECODE_STORED is used to decode a ``stored string'' (see the IDNA specification). It
performs IDN_DECODE_APP plus IDN_UNASCHECK.

The idn_decodename2() function provides the same functionality as idn_decodename() except that character encoding of from is supposed to be auxencoding. If IDN encoding is Punycode and auxencoding is ISO8859-2, for example, it is assumed
that the Punycode string stored in from is written in ISO8859-2.

In the IDN decode procedure, IDN_NAMEPREP is done before IDN_IDNCONV, and some non-ASCII characters are converted to ASCII characters as the result of IDN_NAMEPREP. Therefore, ACE string specified by from might contains
those non-ASCII characters. That is the reason docode_name2() exists.

All of thsee functions return an error value of type idn_result_t. All values other than idn_success indicates some kind of failure.

Name Encoding

Name encoding is a process that transforms the specified internationalized domain name to a certain string suitable for name resolution. For each label in a given domain name, the encoding processor performs:

1.

Convert to UTF-8 (IDN_LOCALCONV)

Convert the encoding of the given domain name from application's local encoding (for example, ISO8859-1) to UTF-8.

Apply character mapping whose rule is determined by the top-level domain name.

4.

NAMEPREP (IDN_NAMEPREP, IDN_UNASCHECK)

Perform name preparation (NAMEPREP), which is a standard process for name canonicalizaion of internationalized domain names.

NAMEPREP consists of 5 steps: mapping, normalization, prohibited character check, bidirectional text check, and unassigned codepoint check. The first four steps are done by IDN_NAMEPREP, and the last step is done by IDN_UNASCHECK.

5.

ASCII range character check (IDN_ASCCHECK)

Checks if the domain name contains non-LDH ASCII characters (not letter, digit, or hyphen characters), or it begins or end with hyphen.

6.

Convert to ACE (IDN_IDNCONV)

Convert the NAMEPREPed name to a special encoding designed for representing internationalized domain names.

The encoding is known as ACE (ASCII Compatible Encoding) since a string in the encoding is just like a traditional ASCII domain name consisting of only letters, digits and hyphens.

7.

Label length check (IDN_LENCHECK)

For each label, check the number of characters in it. It must be in the range of 1 to 63.

Name Decoding

Name decoding is a reverse process of the name encoding. It transforms the specified internationalized domain name in a special encoding suitable for name resolution to the normal name string in the application's current codeset. However, name encoding and name decoding are not symmetric.

For each label in a given domain name, the decoding processor performs:

Perform name preparation (NAMEPREP), which is a standard process for name canonicalizaion of internationalized domain names.

3.

Convert to UTF-8 (IDN_IDNCONV)

Convert the encoding of the given domain name from ACE to UTF-8.

4.

Round trip check (IDN_RTCHECK)

Encode the result of (3) using the Name Encoding scheme, and then compare it with the result of the step (2). If they are different, the check is failed. If IDN_UNASCHECK, IDN_ASCCHECK or both are specified, they are also done in the encoding processes.

5.

Convert to local encoding

Convert the result of (3) from UTF-8 to the application's local encoding (for example, ISO8859-1).

If prohibited character check, unassigned codepoint check or bidirectional text check at step (2) failed, or if round trip check at step (4) failed, the original input label is returned.

Disabling IDN

If your application should always disable internationalized domain name support for some reason, call

(void) idn_enable(0);

before performing encoding/decoding. Afterward, you can enable the support by calling

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3.

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NOTES

The idn_nameinit() function checks internal system configuration files such as /etc/idn/idn.conf and /etc/idn/idnalias.conf if they are in the proper access mode and owership. If they are not in the proper access mode or ownership, the
function will not read and use the configurations defined in the files but use default values. In this case the function will also issue a warning message such as: